To effect cross-pollination between genotypes of plants of the same species, viable pollen grains from the candidate male parent plant must contact stigmata of the candidate female parent at a time when the stigmata are receptive. In plants generally, the stigmata become receptive at approximately the same time the pollen is shed--i.e., at flowering. Not all genotypes of a species of a plant flower at the same length of time after emergence from the soil, so that in cases where the genotypes under consideration as candidate parents for cross-pollination would not naturally flower at the same time, it is necessary to synchronize the flowering to enable cross-pollination. Such may be accomplished by planting the later-flowering prospective parent sufficiently earlier that it flowers at the same time as the earlier-flowering parent, or vice versa. However, such staggered planting is not always sufficiently effective: with respect to some grass crop plants, such as wheat, the seed may be planted in the Fall of the preceding year, with growth resuming the following Spring. Since both candidate parents would resume active growth at approximately the same time, and since both would be vernalized and into the reproductive stage of growth, staggering planting dates has only a small effect on when flowering occurs. Therefore, altering the pollination date by one day may require altering the planting date by ten days. Since it may be necessary to alter the pollination date by several days--i.e., three to twenty-one days, or more--in order to produce certain hybrids, alteration of the planting date as a means of altering the pollination date is impractical on a large scale. Thus, hybridizers do not always have an opportunity for controlling the synchrony of flowering by adjusting planting dates. It is, therefore, desirable that there be some method for synchronizing flowering of plants that is not dependent upon the time of planting.